/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Supplier;

import java.util.concurrent.Callable;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Static utility methods pertaining to the {@link Callable} interface.
 *
 * @author Isaac Shum
 * @since 1.0
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public final class Callables
{
    private Callables()
    {
    }

    /**
     * Creates a {@code Callable} which immediately returns a preset value each time it is called.
     */
    public static <T extends @Nullable Object> Callable<T> returning(@ParametricNullness T value)
    {
        return () -> value;
    }

    /**
     * Creates an {@link AsyncCallable} from a {@link Callable}.
     *
     * <p>The {@link AsyncCallable} returns the {@link ListenableFuture} resulting from {@link
     * ListeningExecutorService#submit(Callable)}.
     *
     * @since 20.0
     */
    @Beta
    @GwtIncompatible
    public static <T extends @Nullable Object> AsyncCallable<T> asAsyncCallable(
            Callable<T> callable, ListeningExecutorService listeningExecutorService)
    {
        checkNotNull(callable);
        checkNotNull(listeningExecutorService);
        return () -> listeningExecutorService.submit(callable);
    }

    /**
     * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
     * running will have the given name.
     *
     * @param callable     The callable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
     *                     for each invocation of the wrapped callable.
     */
    @GwtIncompatible // threads
    static <T extends @Nullable Object> Callable<T> threadRenaming(
            Callable<T> callable, Supplier<String> nameSupplier)
    {
        checkNotNull(nameSupplier);
        checkNotNull(callable);
        return () ->
        {
            Thread currentThread = Thread.currentThread();
            String oldName = currentThread.getName();
            boolean restoreName = trySetName(nameSupplier.get(), currentThread);
            try
            {
                return callable.call();
            }
            finally
            {
                if (restoreName)
                {
                    boolean unused = trySetName(oldName, currentThread);
                }
            }
        };
    }

    /**
     * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
     * running with have the given name.
     *
     * @param task         The Runnable to wrap
     * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
     *                     for each invocation of the wrapped callable.
     */
    @GwtIncompatible // threads
    static Runnable threadRenaming(Runnable task, Supplier<String> nameSupplier)
    {
        checkNotNull(nameSupplier);
        checkNotNull(task);
        return () ->
        {
            Thread currentThread = Thread.currentThread();
            String oldName = currentThread.getName();
            boolean restoreName = trySetName(nameSupplier.get(), currentThread);
            try
            {
                task.run();
            }
            finally
            {
                if (restoreName)
                {
                    boolean unused = trySetName(oldName, currentThread);
                }
            }
        };
    }

    /**
     * Tries to set name of the given {@link Thread}, returns true if successful.
     */
    @GwtIncompatible // threads
    private static boolean trySetName(String threadName, Thread currentThread)
    {
        /*
         * setName should usually succeed, but the security manager can prohibit it. Is there a way to
         * see if we have the modifyThread permission without catching an exception?
         */
        try
        {
            currentThread.setName(threadName);
            return true;
        }
        catch (SecurityException e)
        {
            return false;
        }
    }
}
